A drive mechanism for effecting a movement of a movable element in a machine commonly makes use of a rotatable shaft drivingly connected with the movable element, a drive shaft rotated by a motor and a coupling such as a clutch or gear transmission for drivingly connecting the drive shaft with the rotatable shaft. A precision movement of the movable element is commonly effected in response to a corresponding command drive signal applied to the motor. Movable elements, such as a worktable or tool, in machines often are, however, massive and/or heavy, and impose considerable load on the rotatable shaft. In the operation of a machine, such a movable element normally must encounter varying loads, e.g. machining loads.
Due to these varying loads, it has been recognized that a drive transmission from the motor to the movable element tends to become irregular so that a precision command signal is not necessarily reproduced precisely in a desired movement of the movable element. It is accordingly desirable that a varying load be ascertained within the drive mechanism during a course of operation of the machine.